If the slimehead were still a slimehead, it wouldn't be in this kind of trouble.

An arm-long fish with the look of a prehistoric fossil, the slimehead lived in obscurity a quarter-mile deep in the ocean. The fish was known mainly to scientists, who named it for its distinctive mucus canals.

But then, in the 1970s, seafood dealers came up with a name that no longer tickled the gag reflex. This was the beginning of the "orange roughy."

And, very nearly, the end. With this tasty-sounding name, the slimehead was widely overfished.

On Thursday, a long-awaited report on the world's seafood stocks declared that 63 percent of these species are below healthy levels.

The seafood study, released online Thursday in the journal Science, is one of the most comprehensive looks at the contents of the world's seas. An international group of scientists examined an unprecedented amount of data about harvests and fish populations from the Bering Sea to the Antarctic, and they studied thousands of species from the Atlantic cod to the Australian jackass morwong.

Some of those worst-hit were fish that have been renamed to make them more marketable. For threatened animals on land, a more attractive name might be a blessing. But for these creatures -- slimeheads, goosefish, rock crabs, Patagonian toothfish, whore's eggs -- it was a curse.

That fishermen have turned to them shows what's left in the ocean. Today's seafood is often yesterday's trash fish and monsters.

"People never thought they would be eaten," said Jennifer Jacquet, a biologist at the University of British Columbia. "And as we fish out the world's oceans, we're coming across these species and wondering, 'Can we give them a makeover?' "

The study's lead author, Boris Worm, was following up on a study that predicted that if fishing continued at the same rate, all the world's seafood stocks would collapse by 2048. He said the latest study actually revealed something surprising: a reason for optimism.

About half of the depleted species might actually have a chance to recover, the scientists found, if given enough protection.

But, Worm said, species such as slimehead still illustrate what's gone deeply wrong.

As the world's catch has grown more than fivefold since 1950, he said, overfishing has spread from "rivers to coastal areas to the [continental] shelf to the deep sea." As they went farther and deeper, fishermen have brought back fish that people didn't have recipes -- or even words -- for.

"We didn't even consider fishing [for] these things 15, 20 years ago," said Worm, a professor at Dalhousie University in Canada. Today, he said, "we have another choice. And that is rebuilding what we've lost off our doorstep."

The depleted stocks include familiar fish such as the Atlantic cod, which has been fished so heavily that the Georges Bank population off New England is at 12 percent of healthy levels. The Gulf of Mexico's red snapper stocks are at 6 percent of what scientists say they should be.

To fill the void, some seafood vendors have fraudulently sold cheaper fish as grouper or snapper.

But in other cases, they have given the fish a more palatable name -- preying, environmentalists say, on the arm's-length relationship Americans have with their seafood.

The most famous case involves the Patagonian toothfish and the Antarctic toothfish -- drab, yard-long creatures from the cold waters near the South Pole. In the 1970s, they were rechristened "Chilean sea bass," although they are not, biologically speaking, sea bass.

The toothfish's new name and the firm, oily meat found a huge market. In recent years, environmentalists have said both toothfish are now threatened with heavy fishing, including by "pirate" fishing boats that ignore conservation laws.

The slimehead had similar troubles. Environmentalists say they live long -- 100 years or more -- and reproduce slowly, so it takes a long time to replace fish that are caught.

And along the U.S. Atlantic Coast, fishermen used to toss back a toad-colored fish that looked like it was 30 percent mouth and 50 percent stomach: the goosefish. Then somebody noticed that the tail meat could be cut into tasty fillets. Then, someone thought of "monkfish." Harvests jumped five times from the mid-1980s to the late 1990s, and the fish's numbers dropped.

"You went from unexploited, discarded fish -- bycatch, essentially -- to a targeted species that became overfished," said Thomas Munroe, a zoologist with the National Oceanic and Atmospheric Administration. "The fish was the same as it was as a goosefish."

Federal officials say Chilean sea bass imports are now certified to make sure they came from sustainable operations, that orange roughy are better protected and that monkfish have recovered to safe levels.

But Seafood Watch, a guide produced by the Monterey Bay Aquarium in California, still recommends that consumers avoid Chilean sea bass, orange roughy and monkfish.

Other names have been invented more recently. A few years ago, a Maine seafood dealer renamed the Atlantic rock crab the "peekytoe crab." He's sold hundreds of thousands of pounds since then. A species of sea urchin -- a ball of green spines that Maine lobstermen used to call a whore's egg -- have found a niche in U.S. sushi restaurants under its Japanese name, uni.

Early next year, look for what might be the biggest test yet of the seafoood market's response to a new name. Catfish farmers are going to introduce especially large, thick fillets to white-table restaurants under the name "delacata."

The naming of seafood is policed by the U.S. Food and Drug Administration, which keeps a Seafood List of acceptable market names. One of the more recent additions: snakehead can now be sold as "channa."

But FDA officials said that, in practice, they don't punish many restaurants for calling fish by unsanctioned names. "It is not a high priority . . . unless it involves a food-safety hazard," said Spring Randolph, a consumer safety officer.

At the National Fisheries Institute, a trade group, President John Connelly said the seafood industry works to police itself -- recently going after a California restaurant that was selling a Vietnamese cousin of the catfish as "white roughy." But he said there's nothing wrong with giving new names to unfamiliar creatures.

"A company is always going to find a name that customers are comfortable with," Connelly said. "A cattleman, for instance, doesn't sell 'bull testicles.' They sell 'Rocky Mountain oysters.' "